The present invention is related to Japanese Patent Applications Nos. 11-155464, 11-210499, 11-210500, 11-341476, 2000-199651, and 2000-232208, and claims priority under 35 USC xc2xa7119 to Japanese Patent Application No. 2000-199651, filed on Jun. 30, 2000, and Japanese Patent Application No. 2000-232208, filed on Jul. 31, 2000, the entire contents of all of which is incorporated by reference herein.
1. Field of the Invention
The present invention relates to a chip-type surge absorber for protecting an electronic circuit, a communication device, and the like from a surge such as a lightning surge or noise, and also to a method of producing such a chip-type surge absorber.
2. Discussion of the Background
In order to protect electronic circuits and communication devices from internal or external surges or noise, various types of surge absorbers have been developed and are used effectively. In general, a surge absorber is disposed at a connection point at which an electronic device such as a telephone or a modem is connected to a communication line or is disposed in parallel to a circuit such as a CRT driver circuit or a device which is subject to an electrical impulse such as a lightning surge or electrostatic discharge so as to protect the circuit or the device from the surge by shunting the surge current. In some cases, a surge absorber is disposed in a ground circuit so that a surge current is shunted to ground thereby protecting circuits.
Among various types of surge absorbers, the surge absorber 140 of the type shown in FIG. 13 is widely used because of its good surge response and long life.
The surge absorber of this type is made up of an absorber element enclosed together with a discharge gas within a glass tube 146 sealed at both ends with cap electrodes 143 each having a slag lead 145 wherein the absorber element is made up of a cylindrical-shaped insulator 141 covered with a conductive film 142 having a discharge gap 142A formed at the center thereof.
The principle of operation of the surge absorber 140 is as follows. When a circuit is in a normal operating state, no current flows through the surge absorber 104 because of the existence of the discharge gap 142A formed at the center of the conductive film 142. However, if a surge such as an indirect lightning stroke is input to the circuit, a voltage depending upon the surge is applied across the discharge gap 142A. If this surge voltage is equal to or greater than the discharge start voltage of the surge absorber 140, the discharge gap 142A has an electrical breakdown, and a glow discharge occurs in the discharge gap 142A. If the surge continues further, the temperature of the discharge gas becomes high, and the discharge gas is ionized. Thus, the glow discharge grows into an arc discharge which occurs between the cap electrodes 143. As a result, the surge absorber becomes possible to shunt a greater surge current.
As a result, no surge is applied to the circuit or device which should be protected, and thus the circuit or device is prevented from being damaged. The surge absorber is not damaged fatally only by one discharge, but, in many cases, the surge absorber can withstand a large number of impacts of surges such as about 1000 impacts. In this respect, surge absorbers are very different from fuses which are broken by a single impact of a surge and which must be replaced whenever being broken.
However, the structure of the surge absorber 140 does not allow it to be surface-mounted on a circuit board, because lead wires are necessary for connection with an external circuit. Another problem of the surge absorber 140 is that it is difficult to reduce the size because it is necessary to enclose the cylindrical-shaped insulator 141 within the glass tube 146.
Therefore, the conventional surge absorber 140 does not meet the requirements for electronic circuits with small sizes and high densities.
One technique to overcome the above problems while maintaining the performance of the surge absorber has been proposed in Japanese Unexamined Patent Application Publication No. 8-64336. FIG. 14 illustrates a chip-type surge absorber 150 according to the technique disclosed in Japanese Unexamined Patent Application Publication No. 8-64336 cited above. The chip-type surge absorber 150 includes an insulating substrate 151 in the shape of a rectangular parallelepiped, discharge electrodes 152 formed on the surface of the insulating substrate 151, a discharge gap 153 formed between the discharge electrodes 152, and a pair of terminal electrodes 154 which are electrically connected to the respective discharge electrodes 152 and which are disposed on respective ends of the insulating substrate 151. Furthermore, a hermetic cap 156 is adhesively bonded to the insulating substrate 151 so as to form a hermetically sealed cavity 155 filled with a discharge gas in which the discharge gap 153 and a part of each discharge electrode 152 are enclosed.
The chip-type surge absorber 150 can be surface-mounted on a circuit board by electrically connecting the terminal electrodes to an external circuit via solder. In this chip-type surge absorber 150, the glass tube and the cap electrodes for the purpose of encapsulation are not required, and thus it is possible to reduce the size. The principle of operation is basically the same as that of the surge absorber 140, and thus the surge absorber 150 has similar performance to that of the surge absorber 140.
Although the chip-type surge absorber 150 has the advantage that it can be surface-mounted on a circuit board, the small volume of the hermetically sealed cavity 155 in which a discharge occurs results in small surge resistance.
In the chip-type surge absorber 150, the electrical connection between the discharge electrodes 152 and the corresponding terminal electrodes 154 is realized by forming the discharge electrodes 152 so as to extend to both ends of the insulating substrate 151 and disposing the terminal electrodes 154 directly upon the discharge electrodes 152. To this end, it is necessary that the end faces of the hermetic cap 156 should be at locations shifted inwardly from the ends of the insulating substrate 151 so as to create areas on the insulating substrate 151 where the discharge electrodes 152 are exposed to the outside. However, this results in a reduction in the volume of the hermetically sealed cavity 155. In the chip-type surge absorber 150 shown in FIG. 14, because the surge resistance is proportional to the volume of the hermetically sealed cavity 155, the structure of the chip-type surge absorber 150 results in a reduction in the surge resistance. The above problem may be solved by increasing the surface area of the insulating substrate 151. However, in this case, the resultant penalty is an increase in the mounting area.
The reason why the chip-type surge absorber 150 has the above-described structure is that if the terminal electrodes 154 are formed on the end faces of the insulating substrate 151, it is not assured that the terminal electrodes 154 are electrically connected to the discharge electrodes 154 which are formed, to achieve a long life, so as to have a thickness as small as 1 xcexcm. In particular, in the case where there area plural pairs of discharge electrodes 152, it is very difficult to achieve electrically connection for all pairs of discharge electrodes 152.
In order to trigger the discharge, it is required that electrons which start the discharge be emitted by a high voltage which is induced across the discharge gap by an surge applied to the surge absorber. However, in the chip-type surge absorber 150 shown in FIG. 14 in which there is only one pair of discharge electrodes 152 and there is only one discharge gap 153, there is no particular point where an electric field is concentrated, and thus a delay occurs in starting of the discharge.
Another problem is that the structure of the chip-type surge absorber 150 shown in FIG. 14 is not symmetrical in a vertical direction. Therefore, when the chip-type surge absorber 150 is mounted, it is necessary to correctly place the chip-type surge absorber 150 in the vertical direction. This results in an increase in complexity in the process of automatically mounting chip-type surge absorbers on circuit boards.
Other examples of conventional chip-type surge absorbers are shown in FIGS. 15 and 16.
In the example shown in FIG. 15, the chip-type surge absorber 160 is made up of an insulating substrate 161 having a cavity extending through the insulating substrate 161, a pair of terminal electrodes 162 which are disposed on the respective ends of the insulating substrate 161 such that the above-described cavity is closed by the terminal electrodes 162, a hermetically sealed cavity 163 which is enclosed by the insulating substrate 161 and the terminal electrodes 162 and which is filled with a discharge gas, and a pair of discharge electrodes 165 which are formed within the hermetically sealed cavity 163 and on the insulating substrate 161 such that a discharge gap 164 is formed between the discharge electrodes 165, wherein the terminal electrodes 162 are electrically connected to the corresponding discharge electrodes 165.
On the other hand, in the example shown in FIG. 16, the chip-type surge absorber 170 is made up of an insulating substrate 171 made of alumina or a similar material, discharge electrodes 172 and 173 which are formed at opposing positions on the surface of the insulating substrate 171, a discharge gap 174 formed between the discharge electrodes 172 and 173, a box-shaped hermetic cap 176 made of glass (insulating material) whose peripheral part is adhesively bonded to the insulating substrate 171 such that a hermetically sealed cavity 175 is formed above the discharge electrodes 172 and 173 and such that the hermetically sealed cavity 175 is filled with a discharge gas, and terminal electrodes 177 and 178 which are formed such that both ends of the hermetic cap 176 and both ends of the insulating substrate 171 are covered with the respective terminal electrodes 177 and 178 and such that the discharge electrodes 172 and 173 are electrically connected to the respective terminal electrodes 177 and 178.
If a surge voltage is applied between the discharge electrodes 172 and 173 via the discharge gap 174, a glow discharge is triggered between the discharge electrodes 172 and 173 via the discharge gap 174 as represented by a symbol B in FIG. 16. The discharge grows into a creeping discharge within the hermetically sealed cavity 174 toward the outer-side ends of the discharge electrodes 172 and 173 as represented by arrows C. Finally, the discharge grows into an arc discharge between the discharge electrodes 172 and 173 as represented by an arrow D, which results in absorption of the surge voltage.
There is a need for chip-type surge absorbers which can withstand high surge voltages and thus has high reliability and long life.
In the chip-type surge absorbers 150, 160, and 170 described above, when a surge is applied over a long period of time, a glow discharge grows into an arc discharge between the terminal electrodes. However, because the structure of the chip-type surge absorbers allows low heat dissipation, the arc discharge results in an increase in internal temperature to a few thousands of degrees (centigrade). Because the discharge electrodes are made of ceramic or metal having a high melting point, only one or two discharges do not result in damage. However, when the chip-type surge absorbers are used in circuits which are subject to frequent long-period surges, the electrically conductive film forming the discharge electrodes are damaged by heat generated by the repetition of discharges, and the gap distance of the discharge gap becomes greater. Because the discharge start voltage depends upon the gap distance of the discharge gap, the expansion of the discharge gap results in an increase in the discharge start voltage, which causes an unexpected large voltage to be applied to an electronic circuit or a communication device. Such a high voltage can cause the electric circuit or the communication device to be broken.
When an arc discharge occurs in the chip-type surge absorber, the arc current flows via small points into the outer-side end parts of the discharge electrodes. As a result, local areas near the small points have a very high current density and a high temperature. In the case of the structure shown in FIG. 16 in which the insulating substrate 171 and the hermetic cap 176 are adhesively bonded to each other, the adhesive by which the hermetic cap 176 are connected to each other is melted by the heat, the hermetic cap 176 can be opened. This causes the chip-type surge absorber to be broken by a surge current as small as about 30 A.
Japanese Unexamined Patent Application No. 2000-12186 discloses another chip-type surge absorber.
In this chip-type surge absorber disclosed in Japanese Unexamined Patent Application No. 2000-12186, discharge starting electrodes are formed of diamond under discharge electrodes. One of the inherent properties of diamond is that it has a small work function which allows diamond to easily emit electrons. Therefore, in response to a surge voltage, electrons are emitted by field emission from the discharge starting electrode made of diamond even when the surge voltage is low. Thus, this type of surge absorber can operate at low voltages.
There is also a need for a chip-type surge absorber which operates at a low surge voltage and which can be used in high-frequency circuits.
In the chip-type surge absorbers, because an insulating substrate having a uniform relative dielectric constant is used, the insulating substrate has no particular point where an electric field is concentrated, and the discharge start voltage is determined by the work function of the discharge electrodes employed and by the discharge gas in the hermetically sealed cavity. Therefore, the only way to reduce the discharge start voltage is to properly select the material of the discharge electrodes or the discharge gas.
In the chip-type surge absorber disclosed in Japanese Unexamined Patent Application No. 2000-12186 in which the discharge starting electrodes are formed using diamond, it is necessary to form a thin diamond film using a complicated large-scale apparatus by means of a CVD process or slurry method under precisely controlled process conditions. This makes it difficult to produce this type of surge absorber.
Although not shown, one possible technique to reduce the operating voltage is to form the insulating substrate using a dielectric material having a large relative dielectric constant thereby allowing an electric field to be concentrated. However, this technique results in an increase in the total capacitance, and the insulating substrate acts as a low-pass filter. Therefore, although this type of surge absorber can operate at low voltages, it cannot be used in high-frequency circuits. In other words, it is difficult to realize a chip-type surge absorber which can operate at low voltages and which can be used in high-frequency circuits.
One conventional technique of producing a chip-type surge absorber is described below with reference to FIGS. 17 to 19. First, as shown in FIGS. 17 and 18, discharge electrodes 183 are formed on a heat-resistant electrically-insulating substrate 181 which can provide hermeticity, and a discharge gap 185 with a gap distance of 0.1 to 500 xcexcm is formed between the discharge electrodes 183 by means of laser cutting. A peripheral part of the substrate 181 is then coated with an adhesive 187. A hermetic cap 191 is then placed on the substrate 181 such that an enclosed space 189 serving as a hermetically sealed cavity is formed as shown in FIG. 19. The hermetic cap 191 is adhesively bonded to the substrate 181 such that the discharge gap 185 is located at the center of the enclosed space 189 and such that the far ends of the respective discharge electrodes 183 are exposed to the outside of the hermetic cap 191. The adhesively bonding of the hermetic cap 191 is performed in atmospheric air or in an ambient of an inert gas so that the enclosed space 189 is filled with a desired gas. Finally, terminal electrodes 193 are connected to the externally exposed parts of the respective discharge electrodes 183 as shown in FIG. 20 by means of baking or plating. Thus, the production of the chip-type surge absorber 195 is completed.
In the step of forming the discharge gap 185 according to the above-described conventional production method of the chip-type surge absorber, the gap distance of the discharge gap 185 is adjusted by means of laser cutting such that the discharge start voltage is correctly determined by the gap distance of the discharge gap 185. In the chip-type surge absorber, if the discharge gap 185 is formed so as to have a deep undercut, it becomes possible to prevent the discharge gap 185 from being bridged by conductive dust generated from the discharge electrodes 183, thereby allowing the surge absorber to have a longer absorbing life during which the surge absorber has the surge absorption function.
However, it is difficult to achieve both the reduction in the discharge start voltage and the increase in the life, as described below.
In order to reduce the discharge start voltage, it is necessary to form the discharge gap 185 to have a small gap distance, and thus it is necessary to reduce the laser output power. However, the reduction in the laser output power makes it difficult to form a deep undercut into the substrate 181 made of a refractory material. Thus, the reduction in the discharge start voltage causes a reduction in the life.
Conversely, if the laser cutting is performed with high optical power so as to form a deep undercut into the substrate 181, the life can be increased. However, as the depth of the discharge gap 185 increases, the gap distance of the discharge gap increases. Therefore, in this case, a low discharge start voltage cannot be obtained.
The formation of the deep undercut which is necessary for the increase in life is also difficult for the following reason.
That is, because the substrate 181 made of a refractory material is poor in heat dissipation, heat generated during a discharge can be transferred only through a path formed by the discharge electrodes 183 and the terminal electrodes 193. If the thickness of the discharge electrodes 183 forming the heat transfer path is not sufficiently large, heat is not transferred sufficiently. Therefore, when the chip-type surge absorber is continuously subjected to a plurality of surges, the heat generated cannot be removed sufficiently, and the discharge electrodes 183 are degraded. As a result, a change occurs in the electrical characteristic of the chip-type surge absorber. The above problem can be solved, if the discharge electrodes 183 are formed to have a sufficiently large thickness to obtain good heat dissipation. However, the increase in the thickness of the discharge electrodes 183 makes it difficult to form a deep undercut into the substrate 181.
An object of the present invention is to provide a chip-type surge absorber whose surge resistance is increased without causing an increase in the mounting area.
According to an aspect of the present invention, to achieve the above object, there is provided a chip-type surge absorber including: an insulating substrate in the shape of a rectangular parallelepiped; an insulating hermetic cap open at a bottom side thereof, for forming, together with the insulating substrate, a box-shaped hermetically sealed cavity filled with a discharge gas; terminal electrodes disposed at both ends in the hermetically sealed cavity; a pair of discharge electrodes which are formed in the hermetically sealed cavity such that a discharge gap is formed between the discharge electrodes and such that the discharge electrodes are electrically connected to corresponding terminal electrodes; and connection surfaces for increasing the connection area for the connection between the discharge electrodes and the terminal electrodes.
In this chip-type surge absorber, the discharge electrodes are overlapped with the corresponding terminal electrodes over wide areas thereby assuring good electrical connection between the discharge electrodes and the terminal electrodes even when the discharge electrodes have a small thickness such as 1 xcexcm. This structure allows the hermetic cap to be connected to the insulating substrate such that the ends of the hermetic cap become flush with the corresponding ends of the insulating substrate. As a result, the volume of the hermetically sealed cavity is increased to a maximum possible value, which results in an increase in surge resistance. More specifically, the discharge electrodes extend over the connection surfaces such that the discharge electrodes are overlapped with the corresponding terminal electrodes on the connection surfaces, thereby assuring good electrical connection. Thus, it becomes possible to dispose the hermetic cap such that the ends of the hermetic cap become flush with the corresponding ends of the insulating substrate, thereby increasing the volume of the hermetically sealed cavity, which results in an increase in surge resistance. Another advantage of this chip-type surge absorber is that it has a symmetrical external shape in a vertical direction, and thus it is not necessary, in a mounting process, to distinguish which is an upper side or which is a lower side.
Another object of the present invention is to provide a chip-type surge absorber having large surge resistance and having a small discharge start delay.
According to another aspect of the present invention, to achieve the above object, there is provided a chip-type surge absorber including: an insulating substrate in the shape of a rectangular parallelepiped; an insulating hermetic cap open at a bottom side thereof, for forming, together with the insulating substrate, a box-shaped hermetically sealed cavity filled with a discharge gas; terminal electrodes disposed at both ends in the hermetically sealed cavity; two to five pairs of discharge electrodes which are formed in the hermetically sealed cavity such that a discharge gap is formed between each pair of discharge electrodes and such that the discharge electrodes are electrically connected to the corresponding terminal electrodes; and connection surfaces for increasing the connection area for the connection between the discharge electrodes and the terminal electrodes.
In this chip-type surge absorber, the discharge electrodes are overlapped with the corresponding terminal electrodes over wide areas thereby assuring good electrical connection between the discharge electrodes and the terminal electrodes even when the discharge electrodes have a small thickness such as 1 xcexcm. This structure allows the hermetic cap to be connected to the insulating substrate such that the ends of the hermetic cap become flush with the corresponding ends of the insulating substrate. As a result, the volume of the hermetically sealed cavity is increased to a maximum possible value, which results in an increase in surge resistance. More specifically, the discharge electrodes extend over the connection surfaces such that the discharge electrodes are overlapped with the corresponding terminal electrodes on the connection surfaces, thereby assuring good electrical connection. Thus, it becomes possible to dispose the hermetic cap such that the ends of the hermetic cap become flush with the corresponding ends of the insulating substrate, thereby increasing the volume of the hermetically sealed cavity, which results in an increase in surge resistance. Good electrical connection between the discharge electrodes and the terminal electrodes can be obtained even when there are a large number of pairs of discharge electrodes.
The existence of two to five pairs of the discharge electrodes results in creation of points where an electric field is concentrated when a surge is applied. This allows a discharge to quickly start in response to a surge without having a significant delay. This chip-type surge absorber also has the advantage that it has a symmetrical external shape in a vertical direction, and thus it is not necessary, in a mounting process, to distinguish which is an upper side or which is a lower side.
A still another object of the present invention is to provide a chip-type surge absorber which is not broken by a surge voltage.
According to still another aspect of the present invention, to achieve the above object, there is provided a chip-type surge absorber including an insulating substrate, discharge electrodes which are formed at opposing positions on the insulating substrate such that a discharge gap is formed between the discharge electrodes, a hermetic cap having a peripheral part thereof adhesively bonded to the insulating substrate such that a space above the discharge electrodes is enclosed by the hermetic cap, wherein each of the discharge electrodes has an outer-side end part at a location where the hermetic cap and the insulating substrate are adhesively bonded to each other, and the outer-side end part has a lower electrical resistance than the electrical resistance of the inner-side part of a discharge electrode directly adjacent to the discharge gap.
In this chip-type surge absorber, when a discharge occurs in response to an applied surge voltage, an arc discharge current flows via a particular point of each outer-side end part into the outer-side end parts of the discharge electrodes. However, because the outer-side end parts of the discharge electrodes have a low electrical resistance, the arc current is spread out, and thus the current density of the arc current flowing through the connection part between the hermetical cap and the insulating substrate is reduced, and the increase in temperature is suppressed.
As a result, it becomes possible to prevent the hermetic cap from becoming open by a surge voltage. Thus, the resistance to the surge voltage is improved, and the surge withstanding voltage is increased.
It is still another object of the present invention to provide a chip-type surge absorber having high reliability and a long life.
According to still another aspect of the present invention, to achieve the above object, there is provided a chip-type surge absorber including: an insulating substrate in the shape of a rectangular parallelepiped having a cavity extending through the insulating substrate; a pair of terminal electrodes which are disposed on the respective ends of the insulating substrate such that the cavity is closed by the terminal electrodes; a hermetically sealed cavity which is enclosed by the insulating substrate and the terminal electrodes and which is filled with a discharge gas; and a pair of discharge electrodes which are formed within the hermetically sealed cavity and on one inner surface of the insulating substrate such that a discharge gap is formed between the discharge electrodes, the discharge electrodes being electrically connected with the corresponding terminal electrodes, wherein a relay electrode for relaying an arc discharge is formed within the hermetically sealed cavity and on the other inner surface of the insulating substrate such that the relay electrode is isolated from the discharge electrodes and the terminal electrodes.
In this chip-type surge absorber, if an arc discharge occurs between the terminal electrodes due to a long-period surge, the inside of the hermetically sealed cavity is raised to a high temperature. However, the relay electrode disposed at a location isolated from the discharge electrodes and the terminal electrodes allows the arc discharge to partially occur via the relay electrode. As a result, the arc discharge partially occurs between the relay electrode and the terminal electrodes, and thus the amount of discharge between the discharge electrodes is reduced. This results in a reduction in the amount of discharge between the discharge electrodes. Therefore, a great reduction in the heat load upon the discharge electrodes is achieved. As a result, the discharge gap has high resistance against a large number of surges applied to the discharge gap, and thus the chip-type surge absorber has a long life.
It is still another object of the present invention to provide a chip-type surge absorber having a low discharge start voltage and also having a long life.
According to still another aspect of the present invention, to achieve the above object, there is provided a chip-type surge absorber including: a heat-resistant insulating substrate; a pair of discharge electrodes which are formed on the heat-resistant insulating substrate such that a small gap is formed between the discharge electrodes; and a hermetic cap which is adhesively connected to the insulating substrate such that the small gap is enclosed in a hermetically sealed space formed by the hermetic cap, wherein a stripe-shaped insulating layer having heat resistance lower at least than the heat resistance of the insulating substrate is formed between the insulating substrate and the discharge electrodes.
In this chip-type surge absorber, because the stripe-shaped insulating layer having heat resistance lower at least than the heat resistance of the insulating substrate is formed between the insulating substrate and the discharge electrodes, the insulating layer having low heat resistance is easily cut deeply when the small gap serving as the discharge gap is formed by means of laser cutting. This makes it possible to form the discharge gap so as to have a small gap distance and a large depth. As a result, it becomes possible to obtain a low discharge start voltage, and it also becomes possible to prevent the discharge gap from being filled with electrically conductive dust. Thus, it is possible to achieve both low discharge start voltage and long life at the same time.
It is still another object of the present invention to provide a method of producing a chip-type surge absorber having a low discharge start voltage and also having a long life.
According to still another aspect of the present invention, to achieve the above object, there is provided a method of producing a chip-type surge absorber, including the step of: forming a stripe-shaped insulating layer on a flat substrate surface of a heat-resistant insulating substrate, the insulating layer having lower heat resistance than the heat resistance of the insulating substrate; forming an electrically conductive film having the same stripe shape as the stripe-shaped insulating layer on the stripe-shaped insulating layer having low heat resistance into a multilayer structure; and cutting the electrically conductive film together with the insulating layer having low heat resistance in a direction perpendicular to the longitudinal direction by means of laser cutting, into two portions which serve as a pair of discharge electrodes spaced from each other by a small gap;
In this method of producing the chip-type surge absorber, the insulating layer having low heat resistance is formed on the insulating substrate, and the electrically conductive film formed on the insulating layer having low heat resistance is cut together with the insulating layer into two portions by means of laser cutting. Therefore, the insulating layer having low heat resistance is cut deeply together with the electrically conductive film using a laser with low optical output power. Thus, it is possible to easily obtain a chip-type surge absorber having a discharge gap with a small gap distance and a large depth.
It is still another object of the present invention to provide a chip-type surge absorber which can operate at low voltages and which can be used in high-frequency circuits.
According to still another aspect of the present invention, to achieve the above object, there is provided a chip-type surge absorber including an insulating substrate; discharge electrodes which are formed at opposing positions on the insulating substrate such that a discharge gap is formed between the discharge electrodes; and dielectric layers disposed between the insulating substrate and the respective discharge electrodes, wherein the dielectric layers have a relative dielectric constant greater than that of the relative dielectric constant of the insulating substrate, and at least a part of each of the dielectric layers is exposed in the discharge gap.
In this chip-type surge absorber, because the dielectric layers having a relative dielectric constant greater than the relative dielectric constant of the insulating substrate are formed between the insulating substrate and the respective discharge electrodes such that the dielectric layers are partially exposed in the discharge gap, when a surge voltage is applied, an electric field is concentrated in the dielectric layers via the discharge electrodes, and electrons are emitted from the parts of the electrode in direct connection with the dielectric layers. This allows initial electron emission to start between the discharge electrodes at a low voltage. Therefore, it is possible to achieve a chip-type surge absorber which can operate at a low voltage without having limitations in terms of the work function of the discharge electrodes and in terms of the characteristic of the discharge gas. Furthermore, because the dielectric layers are formed only in limited areas between the insulating substrate and the discharge electrodes such that the dielectric layers are partially exposed in the discharge gap, no increase in capacitance occurs, and therefore this chip-type surge absorber can be employed also in high-frequency circuits.